1. Field of the Invention
The present invention relates to a printer capable of using a plurality of types of continuous form recording sheet having different page lengths.
2. Discussion of Background and Material Information
Dot impact type line printers are generally employed for printing output data from small computers on continuous form recording sheet. Such a line printer is designed to start printing with the storage of printing data on a line basis.
The continuous recording sheet is a so called fan-fold sheet which is foldable and provided with perforation lines. The foldable part is supplied with perforation lines so that the part may be torn off easily. In this case, the printer is often arranged so that it prints data in a portion other than the perforated part, so that the data thus printed is prevented from being cut apart when the paper is torn off.
A printer has been proposed which uses the continuous recording sheet employing an electrophotographic image transfer system for improving printing speed and the like.
Electrophotographic image transferring is the art of printing data through the steps of exposing the charged circumferential surface of a photoconductive drum to light to form a latent image thereon, developing the image thus exposed to light by sticking toner thereon, transferring the image onto the recording sheet, and fixing the image by means of a fixing unit, which may include a heat roller. The electrophotographic transfer system is generally utilized for copying machines and the like.
One such system is a laser beam printer which provides a hard copy of image information by scanning and exposing a photoconductive drum charged by laser beams. The beams are modulated based on image information such as figures, characters and the like, using the copy process of the above electrophotographic method.
The laser beam printer is very useful, because it can be widely used in such a manner that it prints figures of information received by an image reading unit such as an image scanner, or can be used as an output terminal of a facsimile machine, and it can output information at a high speed.
In general, such a laser beam printer conventionally comprises an existing electronic copying machine as a base unit thereof and uses so-called cut-type sheets cut into a predetermined size as a recording sheet. A so-called heat roll type fixing unit which comprises a pair of fixing rollers composed of a heat roller heated to a high temperature and a backup roller pressed thereagainst are provided. A recording sheet on which an unfixed toner image corresponding to the image information is placed, is caused to pass between the rollers so that it is heated and pressed, whereby the toner is melted and adhered on the recording sheet.
Incidentally, the electrophotographic method is such that the rotation of a photoconductive drum causes an exposed portion thereof to reach a transfer unit and a toner image is transferred onto the recording sheet fed at a speed identical to the peripheral speed of the photoconductive drum at the transfer unit. Thus, according to this process it is impossible to form images by intermittently interrupting the process due to the structure of the process.
Therefore, the laser beam printer is provided with a memory capable of storing at least one page of information, and when the one page of information is input therein, the printer outputs the information at one time.
It is of course possible to use this laser beam printer as an output terminal of a computer. In this case, however, the use of a continuous-form sheet similar to that used in a conventional line printer is desired. The continuous-form sheet is used in the conventional line printer is a so-called fan-folded sheet having feed holes and folded along perforated tear lines to enable the sheet to be simply cut off (hereinafter, simply referred to as a "continuous sheet").
When the electrophotographic system is used as a printer using a cut sheet type recording medium, the distance between the transfer and the fixing positions is unimportant, as it is only necessary to consider printer data on a single sheet. In case of a printer using a continuous recording sheet, however, it is important to determine the portion to be fixed. If all of the transferred toner image is fixed when printing is terminated, it wastes a length of sheet equivalent to the aforementioned distance. Consequently, the problem posed then is the extent to which the data transferred onto the recording sheet is fixed.
When printing performance is taken into consideration, the interruption and restart of transfer and fixation respectively should preferably be made such that the perforated part where data to be printed is discontinued is located at the transfer and fixing position. For this reason, perforation lines serving as page-to-page divisions should preferably be located at the transfer and fixing portion when printing is stopped.
With this arrangement, one page of the recording sheet bearing an unfixed toner image is left between the transfer and the fixing position when the printer is on standby condition after a normal printing operation is terminated. When data equivalent to the following one page is transferred, the existing page is subjected to fixation and is discharged. The continuous sheet is thereby prevented from being wasted by not effecting fixation each time a transfer is made.
There are normally two kinds of continuous sheets generally in use; namely, 11-inch and 12-inch long pages. The aforementioned space between the transfer and the fixing position has to be determined, depending on the page length of the sheet in use.
However, it is common that the positional relation between the transfer and the fixing positions has been fixed, and besides the diversified control is exercised in conformity with the fixed paper length. It is consequently impossible in principle for a conventional printer to use a plurality of sheets of paper of different lengths.
Also, when a continuous sheet is used in a laser beam printer using a roll fixing system, the length of a recording sheet feed path from a transfer unit to the fixing position of a fixing unit must be set to be substantially the same as the distance between the perforated tear lines of the continuous sheet in order to prevent a disadvantage, such that when the laser beam printer stops (during a pause or because operation is completed), a page being subjected to a fixing action is stopped in the state that it is held between a pair of fixing rollers, and semi-fixed toner in the process of being fixed remains caught between the pair of fixing rollers.
More specifically, since the continuous-sheet is finally cut off along the perforated tear lines for use, no image must be formed within a predetermined region in the vicinity of the perforated tear lines, and thus in a laser beam printer by which images are formed for each page, the tear lines where no image is formed are arranged to be stopped in the position where they correspond to the transfer unit. Consequently, when the length of the recording sheet feed path from the transfer unit to the fixing position is set to be substantially the same as the distance between the perforated tear lines of the continuous sheet, the above disadvantage can be avoided, because the vicinity of the tear line where no image is formed is caused to correspond to the position of the fixing unit where fixing action is effected, when the laser beam printer stops.
As a result, however, a problem arises in that the printer as a whole is made unnecessarily large in size to provide a necessary feed length for the recording sheet, and a plurality of kinds of continuous sheet, respectively having a different distance between perforated tear lines (i.e., the length of a page), cannot be interchangeably used in this laser beam printer. That is, continuous sheets having a different distance between perforated tear lines cannot be used.